


export function canvasDataURL(path, obj, callback) {
  var img = new Image()
  img.src = path
  img.onload = function() {
    var that = this
    // 默认按比例压缩
    var w = that.width,
      h = that.height,
      scale = w / h
    w = obj.width || w
    h = obj.height || w / scale
    var quality = 0.7 // 默认图片质量为0.7
    //生成canvas
    var canvas = document.createElement('canvas')
    var ctx = canvas.getContext('2d')
    // 创建属性节点
    var anw = document.createAttribute('width')
    anw.nodeValue = w
    var anh = document.createAttribute('height')
    anh.nodeValue = h
    canvas.setAttributeNode(anw)
    canvas.setAttributeNode(anh)
    ctx.drawImage(that, 0, 0, w, h)
    // 图像质量
    if (obj.quality && obj.quality <= 1 && obj.quality > 0) {
      quality = obj.quality
    }
    // quality值越小，所绘制出的图像越模糊
    var base64 = canvas.toDataURL('image/jpeg', quality)
    // 回调函数返回base64的值
    callback(base64)
  }
}